Method and base station for transmitting downlink signal and method and equipment for receiving downlink signal

ABSTRACT

A base station of the present invention configures resources in which a downlink signal is to be transmitted with zero power using resource sets defined for a specific number of antenna ports, regardless of the number of antenna ports actually configured in the base station, and transmits resource information indicating the configured resources to a user equipment. The user equipment of the present invention receives a downlink transmission from the base station, assuming that transmission power of resources corresponding to a resource set indicated by the resource information is zero.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/816,760, filed on Apr. 22, 2013, the entire disclosure ofwhich is hereby incorporated by reference for all purposes as if fullyset forth herein. U.S. patent application Ser. No. 13/816,760 is a U.S.National Stage Entry of PCT International Application No.PCT/KR2011/005783, filed on Aug. 9, 2011, and claims the benefit of U.S.Provisional Application No. 61/373,276, filed on Aug. 13, 2010.

TECHNICAL FIELD

The present invention relates to a method and apparatus fortransmitting/receiving a downlink signal, and more particularly, to amethod and apparatus for configuring resources, in which a signal is tobe transmitted with zero transmission power, i.e., resources to bemuted, and a method and apparatus for transmitting/receiving informationregarding the resources to be muted.

BACKGROUND ART

FIG. 1 illustrates a concept of a cellular wireless communicationsystem.

A number of Base Stations (BSs) are configured so as to cover an entireregion of a specific wireless communication system and each BS isconfigured so as to provide a specific wireless communication service toUser Equipments (UEs) in a corresponding region. All BSs may provide thesame communication service and may also provide different communicationservices. Recent multi-cell wireless communication systems are designedto allow a number of adjacent BSs to communicate with a UE using thesame frequency band.

FIG. 2 illustrates a concept of a wireless communication system usingmultiple sectors in an independent cell.

As described above with reference to FIG. 1, each BS generally providesa communication service to a corresponding geographical region which canbe divided into a plurality of smaller regions Cell 1, Cell 2, and Cell3 in order to improve system performance. Each of the smaller regionsmay be referred to as a cell, a sector, or a segment. Signalinterference may not only occur between cells belonging to different BSsas shown in FIG. 1 but may also occur between cells belonging to thesame BS as shown in FIG. 2.

The overall performance of the wireless communication system may bereduced if the influence of interference caused by adjacent cells is nottaken into consideration in the multi-cell system. For example,referring to FIG. 2, if a specific UE is located between BS1 and BS2,signals that the BS1 and BS2 transmit to the specific UE using the samefrequency band affect the specific UE at similar strengths. A downlinksignal of the BS1 and a downlink signal of the BS2 cause interference toeach other. If a communication system is configured without taking intoconsideration the influence of such interference, there is a problem inthat it is not possible to optimize system throughput since channelstate information (also referred to as channel quality information) thatthe UE feeds back to the BS is incorrect.

As a result, in order to optimize throughput of such a communicationsystem, it is important to configure a communication system so as toallow the UE to correctly measure a channel state between an adjacentcell and the UE and/or to correctly measure a channel state of a servingcell taking into consideration the level of interference caused byadjacent cells.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, there is a need to provide a method for minimizing theinfluence of inter-cell interference and a method for increasing theaccuracy of measurement of a channel state of each cell and/ormeasurement of interference of an adjacent cell exerted upon each cell.

Objects of the present invention are not limited to those describedabove and other objects will be clearly understood by those skilled inthe art from the following detailed description of the presentinvention.

Solution to Problem

A transmission device of the present invention configures resources inwhich a signal is to be transmitted with zero power using resource setsdefined for a specific number of antenna ports, regardless of the numberof antenna ports actually configured in the transmission device, andtransmits resource information indicating the configured resources to areception device. The reception device of the present invention receivesa signal transmission from the transmission device, assuming thattransmission power of resources corresponding to a resource setindicated by the resource information is zero.

In more detail, in an aspect of the present invention, a method fortransmitting a downlink signal from a Base Station (BS) in a wirelesscommunication system in which resource sets for a reference signal forchannel measurement are defined according to the number of antenna portsis provided. The method comprises: configuring a zero transmission powerregion in a resource region including a plurality of resources;transmitting resource information indicating the zero transmission powerregion to a User Equipment (UE); and performing downlink transmission tothe UE in the resource region, wherein the zero transmission powerregion is configured with at least one of a plurality of resource setsdefined for reference signal transmission for channel measurement for aspecific number of antenna ports regardless of the number of antennaports configured in the BS, and wherein transmission power for resourcescorresponding to the zero transmission power region is zero.

In another aspect of the present invention, a method for receiving adownlink signal by a User Equipment (UE) in a wireless communicationsystem in which resource sets for a reference signal for channelmeasurement are defined according to the number of antenna ports isprovided. The method comprises: receiving resource informationindicating a zero transmission power region in a resource regionincluding a plurality of resources from a Base Station (BS); andreceiving a downlink transmission from the BS in the resource region,wherein the zero transmission power region is configured with at leastone of a plurality of resource sets defined for reference signaltransmission for channel measurement for a specific number of antennaports regardless of the number of antenna ports configured in the BS,and wherein the UE receives the downlink transmission, assuming based onthe resource information that transmission power of resourcescorresponding to the zero transmission power region is zero.

In a further aspect of the present invention, a Base Station (BS) fortransmitting a downlink signal in a wireless communication system inwhich resource sets for a reference signal for channel measurement aredefined according to the number of antenna ports is provided. The BScomprises: a transmitter; and a processor electrically connected to thetransmitter and configured to control the transmitter, wherein theprocessor configures a zero transmission power region in a resourceregion including a plurality of resources, controls the transmitter totransmit resource information indicating the zero transmission powerregion to a User Equipment (UE), and controls the transmitter to performdownlink transmission to the UE in the resource region, wherein theprocessor configures the zero transmission power region using at leastone of a plurality of resource sets defined for reference signaltransmission for channel measurement for a specific number of antennaports regardless of the number of antenna ports configured in the BS,and wherein the processor controls the transmitter to perform thedownlink transmission at zero transmission power on resourcescorresponding to the zero transmission power region.

In still another aspect of the present invention, a User Equipment (UE)for receiving a downlink signal in a wireless communication system inwhich resource sets for a reference signal for channel measurement aredefined according to the number of antenna ports is provided. The UEcomprises: a receiver; and a processor electrically connected to thereceiver and configured to control the receiver, wherein the processorcontrols the receiver to receive resource information indicating a zerotransmission power region in a resource region including a plurality ofresources from a Base Station (BS), and controls the transmitter toreceive a downlink transmission from the BS in the resource region,wherein the zero transmission power region is configured with at leastone of a plurality of resource sets defined for reference signaltransmission for channel measurement for a specific number of antennaports regardless of the number of antenna ports configured in the BS,and wherein the processor is configured so as to assume based on theresource information that transmission power of resources correspondingto the zero transmission power region is zero.

In each aspect of the present invention, the resource information mayinclude a plurality of bits corresponding respectively to the pluralityof resource sets defined for the specific number of antenna ports, and abit corresponding to a resource set included in the zero transmissionpower region among the plurality of bits may be set to a first value anda bit corresponding to a resource set that is not included in the zerotransmission power region may be set to a second value.

In each aspect of the present invention, the resource sets defined inthe wireless communication system may include at least first resourcesets defined for reference signal transmission for channel measurementfor N1 antenna ports and second resource sets defined for referencesignal transmission for channel measurement for N2 antenna ports,wherein N2 is greater than N1, and the specific number may be N2.

The above-described technical solutions are only part of the embodimentsof the present invention and those having ordinary knowledge in the artwill be able to derive and understand various embodiments incorporatingtechnical features of the present invention from the detaileddescription of the present invention.

Advantageous Effects of Invention

According to the present invention, it is possible to efficientlyconfigure resources for channel measurement and/or interferencemeasurement.

In addition, it is possible to reduce overhead required for transmissionof information indicating muted resources.

Advantages of the present invention are not limited to those describedabove and other advantages will be clearly understood by those skilledin the art from the following detailed description of the presentinvention.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates a concept of a cellular wireless communicationsystem;

FIG. 2 illustrates a concept of a wireless communication system usingmultiple sectors in an independent cell;

FIG. 3 illustrates a CSI-RS pattern;

FIG. 4 illustrates resource muting and a muting configurationinformation according to the first embodiment of the present invention;

FIG. 5 illustrates resource muting and a muting configurationinformation according to the second embodiment of the present invention;

FIG. 6 illustrates another example of resource muting and mutingconfiguration information according to the second embodiment of thepresent invention;

FIG. 7 illustrates resource muting and a muting configurationinformation according to the third embodiment of the present invention;

FIG. 8 illustrates another example of resource muting and mutingconfiguration information according to the third embodiment of thepresent invention;

FIGS. 9 to 11 illustrate resource muting and muting configurationinformation according to the fifth embodiment of the present invention;and

FIG. 12 is a block diagram of a UE and a BS for implementing the presentinvention.

MODE FOR THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following detaileddescription includes specific details in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout such specific details.

In some instances, known structures and devices are omitted or shown inblock diagram form, focusing on important features of the structures anddevices, so as not to obscure the concept of the present invention. Thesame reference numbers will be used throughout this specification torefer to the same or like parts.

In the present invention, the term “User Equipment (UE)” refers to anyof various devices that may be stationary or mobile and may communicatewith a BS to transmit and receive user data and/or various controlinformation to and from the BS. The UE may also be referred to as aterminal equipment, a mobile station (MS), a mobile terminal (MT), auser terminal (UT), a subscriber station (SS), a wireless device, apersonal digital assistant (PDA), a wireless modem, or a handhelddevice. In addition, in the present invention, the term “Base station(BS)” generally refers to a fixed station that communicates with a UEand/or another BS to exchange various data and control information. TheBS may also be referred to by other terms such as an evolved-NodeB(eNB), a base transceiver system (BTS), or an access point (AP).

In the present invention, the term “cell” refers to a geographicalregion to which a BS or an antenna group provides a communicationservice. Thus, when it is said that an entity communicates with aspecific cell, it means that the entity communicates with an antennagroup that provides a communication service to the specific cell. Theterm “downlink/uplink signal of a specific cell” refers to adownlink/uplink signal with respect to an antenna group that provides acommunication service to the specific cell. The term “channelstate/quality of a specific cell” refers to a channel state/quality of acommunication link or a channel established between a UE and an antennagroup that provides a communication service to the specific cell. In thepresent invention, when it is said that a specific signal is allocatedto a frame, subframe, slot, carrier, or subcarrier, this means that thespecific signal is transmitted through the carrier or subcarrier duringa period or timing of the frame, subframe, slot, or symbol.

In addition, in the present invention, the term “resource element (RE)”refers to the minimum time-frequency resource unit which includes anOFDM symbol and a subcarrier. The RE may also be referred to as a tone.An RE in which a reference signal is transmitted is referred to as an RSRE and an RE in which control information or data is transmitted isreferred to as a data RE.

In the present invention, the term “frame” refers to a structured datasequence that has a fixed duration used in some physical (PHY) layerstandards. One frame may include one or more subframes which are basicunits of Transmission Time Intervals (TTIs). Generally, a basic TTI isset as one subframe. The term “TTI” refers to a time interval in whichan encoded packet is transmitted through a radio interface in thephysical layer. Thus, the TTI may be used when one subframe or aplurality of adjacent subframes transmits a data packet. The subframemay include a plurality of OFDM symbols in the time domain and include aplurality of subcarriers in the frequency domain.

Hereinafter, if no signal is transmitted within a frame, subframe, aslot, a symbol, a carrier, a subcarrier, or a resource element, it maybe said that the frame, subframe, slot, symbol, carrier, subcarrier, orresource element has been muted, nulled, or blanked. For example, if atransmitter has set the transmission power of a specific resource unit(also referred to as a specific resource) to zero, it may be said thatthe transmitter has muted, nulled, or blanked the specific resourceunit. That is, the transmitter does not transmit any signal throughmuted, nulled, or blanked resources.

The embodiments of the present invention can be supported by thestandard documents disclosed in at least one of the wireless accesssystems including an Institute of Electrical and Electronics Engineers(IEEE) 802 system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, a 3GPP LTE-Advanced (LTE-A)system, and a 3GPP2 system. That is, the steps or portions, which arenot described in order to make the technical spirit of the presentinvention clear, may be supported by the standard documents. Inaddition, all terms disclosed in the present document can be explainedby the above standard documents.

Techniques, apparatuses and systems described in the following can beused in various wireless access systems. Examples of the variouswireless access systems include a Code Division Multiple Access (CDMA)system, a Frequency Division Multiple Access (FDMA) system, a TimeDivision Multiple Access (TDMA) system, an Orthogonal Frequency DivisionMultiple Access (OFDMA) system, a Single Carrier Frequency DivisionMultiple Access (SC-FDMA) system, and a Multi-Carrier Frequency DivisionMultiple Access (MC-FDMA) system. CDMA may be implemented with a radiotechnology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented with a radio technology such as GlobalSystem for Mobile communications (GSM), General Packet Radio Service(GPRS), or Enhanced Data rates for GSM Evolution (EDGE). OFDMA may beimplemented with a radio technology such as Institute of Electrical andElectronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, or Evolved-UTRA (E-UTRA). UTRA is a part of Universal MobileTelecommunication System (UMTS) and 3rd Generation Partnership Project(3GPP) Long Term Evolution (LTE) is a part of Evolved-UMTS (E-UMTS) thatuses E-UTRA. 3GPP LTE employs OFDMA for downlink and employs SC-FDMA foruplink. LTE-Advanced (LTE-A) is an evolved version of 3GPP LTE. For easeof explanation, the present invention will hereinafter be describedmainly using terms used in the 3GPP LTE/LTE-A. However, technicalfeatures of the present invention are not limited to the 3GPP LTE/LTE-Asystem. For example, although the following description will be givenbased on a mobile communication system corresponding to the 3GPPLTE/LTE-A system, the following description can be applied to othermobile communication systems, excluding unique features of the 3GPPLTE/LTE-A system.

<Reference Signal (RS)>

Various RSs are transmitted between the BS and UE for the purposes suchas alleviation of interference, estimation of a channel state betweenthe BS and UE, and demodulation of a signal transmitted between the BSand the UE. The RS is a signal which has a predefined special waveformknown to both the BS and UE and which is transmitted from the BS to theUE or from the UE to the BS. The RS is also referred to as a pilot.

RSs may be mainly classified into a dedicated RS (DRS) and a common RS(CRS). RSs may also be mainly classified into an RS for demodulation andan RS for channel measurement. The CRS and the DRS may also be referredto as a cell-specific RS and a demodulation RS (DMRS). The DMRS may alsobe referred to as a UE-specific RS.

The CRS is an RS that can be used for both demodulation and measurementpurposes and is common to all UEs in the cell. On the other hand, theDRS is generally used only for demodulation purposes and can be usedonly by a specific UE.

In the case of CRS based downlink transmission, the BS transmits a CRSfor channel estimation between the UE and the BS and a DRS fordemodulation of a layer while transmitting the layer to the UE. The CRSsequence is transmitted through all antenna ports regardless of thenumber of layers. The CRS is transmitted in all subframes that supportdownlink transmission since the CRS is used for both demodulation andmeasurement purposes. Accordingly, CRS based downlink transmissionincreases overall RS overhead as the number of physical antenna portsincreases, thereby reducing data transmission efficiency.

In order to overcome this problem, the present invention suggests thatan RS for modulation and an RS for channel measurement be discriminatelyused instead of using a CRS which increases transmission overhead as thenumber of antenna ports increases since it is used for both channelestimation and data demodulation.

The UE may measure a channel state/quality of a corresponding cell usingan RS for channel measurement and may demodulate downlink datatransmitted to the UE using an RS for demodulation.

<RS for Channel Measurement>

In the following, the present invention suggests a method forconfiguring an RS for channel estimation so as to measure a channelstate of each cell and/or interference of an adjacent cell caused toeach cell while minimizing inter-cell interference and a method formeasuring channel state and/or interference using such RS for channelestimation. In the following description of embodiments of the presentinvention, the RS for channel estimation is referred to as a channelstate information RS (CSI-RS).

The variation of channel state with time is not relatively great. Datathroughput decreases as RS overhead increases since resources used forRS transmission cannot be used for data transmission. Taking intoconsideration this fact, a CST-RS is configured so as to be transmittedat intervals of a predetermined period spanning a plurality ofsubframes, unlike a CRS that is configured so as to be transmitted everysubframe. In this case, there is an advantage in that CSI-RStransmission overhead may be greatly reduced compared to CRStransmission overhead. Accordingly, in the present invention, the BStransmits CSI-RS(s) to a UE located in a cell, to which the BS transmitsa communication service, at intervals of a transmission period spanninga plurality of subframes rather than every subframe.

The BS transmits a CSI-RS or CSI-RSs through a specific antenna groupincluding one or more antennas belonging to the BS at intervals of theCSI-RS transmission period in order for a UE to measure a channelestablished with the specific antenna group. A UE, which receives acommunication signal from the specific antenna group, may receive aCSI-RS transmitted from each antenna port in the specific antenna groupand then estimate/measure state/quality of a channel established betweenthe specific antenna group and the UE. The UE may feed channel stateinformation indicating the result of the channel measurement back to theBS.

In the following description, the term “CSI-RS resource” or “CSI-RS RE”refers to an RE that can be allocated or is available for CSI-RStransmission. A symbol/carrier/subcarrier to which a CSI-RS is allocatedis referred to as a CSI-RS symbol/carrier/subcarrier. For example, asymbol to which a CSI-RS is allocated is referred to as a CSI-RS symboland a subcarrier to which a CSI-RS is allocated is referred to as aCSI-RS subcarrier. A subframe in which CSI-RS transmission is configuredis referred to as a CSI-RS subframe. A subframe in which a mutedresource is configured is referred to as a muting subframe.

In addition, an antenna port transmitting a CSI-RS from among theantenna port(s) of the BS is referred to as a CSI-RS antenna port. A BSincluding N_(t) antenna ports may configure up to N_(t) CSI-RS ports forCSI-RS transmission. All antenna ports in the BS become CSI-RS antennaports when all the antenna ports transmit a CSI-RS and a specificantenna port becomes a CSI-RS antenna when the specific antenna porttransmits a CSI-RS/DRS. Each CSI-RS port transmits a correspondingCSI-RS through a corresponding time-frequency resource (or resourceunit).

The BS may transmit one or more CSI-RSs through one or more antennaports in a cell-specific manner and the UE may measure a channel of thecell by receiving the CSI-RS(s) of the cell. The UE may feed channelstate information indicating a result of the channel measurement back tothe BS.

CSI-RS positions of adjacent cells should not overlap in order toprevent collision of CSI-RSs transmitted between multiple cells and toprevent a CSI-RS to be transmitted by each cell from being dropped dueto resource muting. Accordingly, it is desirable that resources to whichCST-RSs of adjacent cells are allocated be orthogonal to each other.Such CSI-RS orthogonality may also be achieved by mapping CSI-RSstransmitted by adjacent cells to radio resources so as to prevent theCSI-RSs transmitted by adjacent cells from overlapping in anytime/frequency resource region. In the following description, a resourceposition or a set of resources in a specific resource region (forexample, a resource block pair) in which CSI-RS port(s) configured bythe BS transmit CSI-RS(s) will be referred to as a CSI-RS pattern. Forreference, the CST-RS pattern will also be referred to as a CST-RSconfiguration.

FIG. 3 illustrates a CSI-RS pattern. For ease of explanation, it isassumed that the BS may configure up to 8 CSI-RS ports. In addition,although it is assumed in FIG. 3 that a CSI-RS pattern is defined in aresource region including 12 subcarriers and 14 OFDM symbols, the numberof subcarriers and OFDM symbols included in the resource region in whichthe CSI-RS pattern is defined may vary depending on the mobilecommunication system.

Specifically, FIG. 3(a) illustrates 20 CSI-RS patterns that areavailable for CSI-RS transmission through 2 CSI-RS ports, FIG. 3(b)illustrates 10 CSI-RS patterns that are available for CSI-RStransmission through 4 CSI-RS ports, and FIG. 3(c) illustrates 5 CSI-RSpatterns that are available for CSI-RS transmission through 8 CSI-RSports. A respective number may be assigned to each CSI-RS patterndefined according to the number of CSI-RS ports.

When the BS configures 2 antenna ports for RS transmission for channelmeasurement, i.e., when the BS configures 2 CSI-RS ports, the 2 CSI-RSports transmit CSI-RSs on radio resources belonging to one of the 20CSI-RS patterns shown in FIG. 3(a). When the BS configures 4 CSI-RSports for a specific cell, the 4 CSI-RS ports transmit CSI-RSs on aCSI-RS pattern configured for the specific cell from among the 10 CSI-RSpatterns shown in FIG. 3(b). Similarly, when the BS configures 8 CSI-RSports for a specific cell, the 8 CSI-RS ports transmit CSI-RSs on aCSI-RS pattern configured for the specific cell from among the 5 CSI-RSpatterns shown in FIG. 3(c).

In a multi-cell system, BS(s) of adjacent cells that participate inchannel measurement and/or channel interference measurement may preventcollision of CSI-RS transmission by configuring different CSI-RSpatterns for the adjacent cells. In the following description, a set ofcells that participate in channel measurement and/or interferencemeasurement is referred to as an estimation set. Here, it is preferablethat CSI-RS patterns whose time-frequency resources do not overlap beassigned to cells in a specific estimation set.

To receive a CSI-RS transmitted by the BS and to perform channelmeasurement using the CSI-RS, the UE needs to be aware of a resourcethrough which the CSI-RS is transmitted. That is, to detect a CSI-RSthat the BS of the serving cell transmits on a CST-RS pattern, it isnecessary for the UE to know the CSI-RS pattern of the serving cell.Accordingly, the BS transmits CSI-RS configuration informationspecifying the CSI-RS pattern to UE or UEs within the coverage of theBS.

<Resource Muting>

On the other hand, in order to allow the UE to more correctly measure achannel state of a specific cell (or a specific antenna grouptransmission point), cells adjacent to the specific cell may nottransmit a signal through a CST-RS subcarrier in an OFDM symbol in whicha CSI-RS is transmitted in the specific cell. This is referred to asresource muting, RE muting, or time-frequency resource muting. If aspecific resource is muted in a specific cell, there is an advantage inthat the specific cell has no influence upon channel estimation and/orinterference measurement that the UE performs through the specificresource since a downlink signal of the specific cell is not transmittedto the UE through the specific resource. That is, it is possible toexclude the influence of a signal transmitted through the specific cellin the channel measurement and/or interference measurement procedure.

Resource muting is generally used to mute, in the serving cell, the samedata RE as that of a CSI-RS pattern of an adjacent cell, which is to beestimated, to allow a CSI-RS transmitted from the adjacent cell to bedetected without interference caused by a data signal of the servingcell. Accordingly, resource muting is generally applied to REs allocatedto CSI-RS(s) of other cell(s).

To perform correct channel measurement and interference measurement, itis necessary for the UE to be aware of which radio resource is muted. Inorder to correctly demodulate received data, the receiving end generallyperforms rate matching to collect actual data REs from among REs in thedata region. When a CSI-RS has been configured or resource muting hasbeen configured, the UE handles the muted REs and the CSI-RS REs fromamong REs in the corresponding subframe as non-data REs in the ratematching procedure. Accordingly, even when resources muted by theserving cell are not resources through which an adjacent cell transmitsa CSI-RS, the UE needs to know which radio resource has been muted inorder to correctly demodulate received data. Since the UE receives, fromthe BS, information regarding the CSI-RS pattern of a cell (i.e., theserving cell) in which the UE is located, it is possible for the UE todetermine a CSI-RS pattern through which a CSI-RS for measurement of thechannel between the UE and the BS is to be transmitted. However, sincethe UE generally does not know a CSI-RS pattern used by an adjacentcell, there is a problem in that it is difficult to determine whichresource is to be muted by the BS of the serving cell. Accordingly, itis desirable that the BS transmit, to the UE, information indicating aradio resource which is to be muted by the serving cell of the UE. Thisinformation will hereinafter be referred to as muting configurationinformation or muting pattern information.

Thus, downlink overhead for transmission of muting configurationinformation inevitably occurs in the case where the BS supports resourcemuting. Accordingly, there is a need to provide a method for efficientlytransmitting muting configuration information, which is a kind ofcontrol information, from the BS to the UE.

<Muting Pattern>

If the BS can arbitrarily select and mute radio resources in a specificresource region, overhead for transmitting information specifying anarbitrarily selected muting resource to the UE is very great.Accordingly, it is preferable to predefine a set of radio resources thatcan be muted. In the following description, a resource position or aresource set, through which all antenna ports of a serving cell (orserving BS) transmit a signal with zero transmission power (i.e.,transmit no signal) in a specific resource region (for example, aresource block pair of the 3GPP LTE standard or a tile according to theIEEE 802.16 standard), is referred to as a muting pattern or an REmapping pattern. When resource muting of the serving cell is configured,there is a high possibility that the BS will mute the same data RE as aCSI-RS pattern of an adjacent cell to be estimated. Accordingly, it isdesirable that the muting pattern be configured taking intoconsideration the CSI-RS pattern. In the following, embodiments of thepresent invention of transmission of muting configuration informationfrom the BS are described assuming that the muting pattern is configuredbased on the CSI-RS patterns of FIG. 3.

First Embodiment: Bitmap-Based Muting Configuration

In the first embodiment of the present invention, different CSI-RSpatterns are freely allocated to cells belonging to an estimation set.That is, as long as the cells belonging to the estimation set and thecorresponding CSI-RS patterns are in one-to-one correspondence, the samenumber of CSI-RS patterns as the cells belonging to the estimation setmay be arbitrarily selected from among the predefined CSI-RS patterns.The BS may mute CSI-RS patterns other than CSI-RS patterns to be usedfor CSI-RS transmission to a specific coverage and may signal the mutedCSI-RS patterns among the predefined CSI-RS patterns to the UE using abitmap. For example, when the total number of CS1-RS patterns that canbe selected by the BS is n, the BS can transmit muted CSI-RS patternsamong the n CSI-RS patterns to the UE using an n-bit bitmap. Assumingthat the number of CSI-RS ports is separately signaled to the UE,referring to FIG. 3(a), it is possible to configure, as mutingconfiguration information, a bitmap including 20 bits correspondingrespectively to 20 CSI-RS patterns since the total number of CSI-RSpatterns for 2 CSI-RS ports is 20. Referring to FIG. 3(b), it ispossible to configure, as muting configuration information, a bitmapincluding 10 bits corresponding respectively to 10 CSI-RS patterns sincethe total number of CSI-RS patterns for 4 CSI-RS ports is 10, and,referring to FIG. 3(c), it is possible to configure, as mutingconfiguration information, a bitmap including 5 bits since the totalnumber of CSI-RS patterns for 8 CSI-RS ports is 5.

FIG. 4 illustrates resource muting and muting configuration informationaccording to the first embodiment of the present invention.Specifically, FIG. 4 shows muting configuration information that the BScan transmit to the corresponding coverage when 8 CSI-RS ports areconfigured in the BS.

Referring to FIGS. 3(c) and 4, the BS of the serving cell may determinea CSI-RS pattern to be muted through negotiation with a BS of anadjacent cell that causes a strong interference signal to the servingcell or receives strong interference by a signal from the serving cell.For example, in the case where CSI-RSs of cells adjacent to the servingcell to which the BS needs to transmit a CSI-RS are transmitted througha CSI-RS pattern 1 and a CSI-RS pattern 4, the base station of theserving cell may configure a muting pattern so as to mute REs belongingto the CSI-RS pattern 1 and the CSI-RS pattern 4. In order to indicatethe muting pattern, the BS may transmit a bitmap including 5 bits“01001” in which bits corresponding to the CSI-RS pattern 1 and theCSI-RS pattern 4 are set to “1” and the remaining bits are set to “0”.

In the case where a UE has received a bitmap set to “01001” from a BS,the UE performs interference measurement and/or rate matching, assumingthat the BS has not transmitted a signal through REs belonging to theCSI-RS pattern 1 and the CSI-RS pattern 4. That is, when measuringinterference, the UE may handle a signal detected through the CSI-RSpattern 1 and the CSI-RS pattern 4 as an interference signal or noise.The UE may exclude a signal detected through REs belonging to the CSI-RSpattern 1 and the CSI-RS pattern 4 from data to be demodulated in therate matching procedure, assuming that the REs belonging to the CSI-RSpattern 1 and the CSI-RS pattern 4 are not data REs. The UE handles, asdata REs, REs belonging to the CSI-RS pattern 0, the CSI-RS pattern 2,and the CSI-RS pattern 3 which have been set to “0” in the bitmap unlessthe REs belonging to the CSI-RS pattern 0, the CSI-RS pattern 2, and theCSI-RS pattern 3 are used for transmission of a different type of RS ora synchronous signal. For example, in the case where the BS configures 2CSI-RS ports and uses the CSI-RS pattern 2 of FIG. 3(a) for CSI-RStransmission, the UE may handle, as data REs, REs other than REsbelonging to the CSI-RS pattern 2 of FIG. 3(a) from among the CSI-RSpattern 0, the CSI-RS pattern 2, and the CSI-RS pattern 3 which havebeen set to 0 in the bitmap. For reference, the UE may handle a signalreceived through the CSI-RS pattern 2 of FIG. 3(a) as a CSI-RS and mayperform channel measurement using the CST-RS.

In the case where a muting pattern is signaled using a bitmap, there isan advantage in that the BS can configure various muting patterns. Thenumber of CSI-RS patterns that the BS mutes varies depending on thenumber of adjacent cells belonging to an estimation set. In the casewhere no adjacent cell is included in the estimation set or the servingcell has little influence upon adjacent cells, the BS may not configureresource muting. In addition, the BS may configure resource muting so asto mute all resources covered by CSI-RS patterns defined in a wirelesscommunication system to which the BS belongs.

In the case where a total of n CSI-RS patterns are predefined, thenumber of resource muting patterns that can be configured by the BS maybe expressed as follows, including the case in which no CSI-RS patternis muted.

$\begin{matrix}{{{MathFigure}{\mspace{11mu}\;}1}\mspace{425mu}{\sum\limits_{i = 0}^{n}\;\begin{pmatrix}n \\i\end{pmatrix}}} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

However, if a CSI-RS and muting are configured in the same subframe, aCSI-RS pattern used for CST-RS transmission of the serving cell needs tobe excluded from muting and therefore the number of resource mutingpatterns that the BS can configure in the subframe may be expressed asfollows.

$\begin{matrix}{{{MathFigure}{\mspace{11mu}\;}2}\mspace{425mu}{\sum\limits_{i = 0}^{n - 1}\;\begin{pmatrix}n \\i\end{pmatrix}}} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

Signaling of muting configuration information using a bitmap has anadvantage in that resource muting can be completely flexibly configured.However, since the number of bits of the bitmap is proportional to thenumber of CSI-RS patterns, muting configuration information transmissionusing a bitmap has a higher signaling overhead for rate mating andresource mapping than that of the second and third embodiments describedbelow.

Second Embodiment: Tree-Based Muting Configuration

In the second embodiment of the present invention, a muting pattern isconfigured by muting consecutive CSI-RS patterns from among predefinedCSI-RS patterns. A BS which participates in channel measurement and/orinterference measurement cooperates with an adjacent BS whichparticipates in the channel measurement and interference measurement toallow the adjacent BS to transmit a CST-RS of the adjacent CSI-RS withinresources belonging to the muted CSI-RS patterns.

FIG. 5 illustrates resource muting and muting configuration informationaccording to the second embodiment of the present invention.

All muted CSI-RS patterns may be notified to the UE through tree-basedsignaling. For example, the BS may be configured to configure a mutingpattern by muting consecutive CSI-RS patterns.

Referring to FIG. 5, in the case where the BS mutes a range of CST-RSpatterns from CSI-RS pattern 1 to CSI-RS pattern 2, the BS may transmitmuting configuration information corresponding to the starting CSI-RSpattern 1 and the ending CSI-RS pattern 2 to the UE.

By receiving the muting configuration information, a UE located in thecoverage of the BS can determine that REs belonging to the range ofCSI-RS patterns from the CSI-RS pattern 1 to the CSI-RS pattern 2 aremuted. The UE performs rate matching, assuming that the BS transmits nosignal through the REs belonging to the range of CSI-RS patterns fromthe CSI-RS pattern 1 to the CSI-RS pattern 2. That is, the UE assumesthat transmission powers of the REs belonging to the range of CSI-RSpatterns from the CSI-RS pattern 1 to the CSI-RS pattern 2 are zero.Accordingly, the REs belonging to the CSI-RS pattern 1 and the CSI-RSpattern 2 are handled as non-data REs in the rate matching procedure.The REs belonging to the CSI-RS pattern 1 and the CSI-RS pattern 2 mayalso be used for CSI-RS transmission of an adjacent cell.

FIG. 6 illustrates another example of resource muting and mutingconfiguration information according to the second embodiment of thepresent invention.

A wireless communication system may be configured so as to allow cellsbelonging to a specific estimation set to use consecutive CSI-RSpatterns. In this case, BS(s) that participate in channel measurementand/or interference measurement may select a starting CSI-RS pattern andan ending CSI-RS pattern for cells belonging to the estimation set toperform CSI-RS configuration for the channel measurement and/orinterference measurement. The serving BS may transmit, to the UE, mutingpattern information corresponding to the starting CSI-RS pattern and theending CSI-RS pattern and the CSI-RS pattern used for CSI-RStransmission of the serving cell.

For example, let us assume that the BS configures CSI-RS transmissionusing consecutive CSI-RS patterns 1, 2, and 3 while the BS mutes theCSI-RS patterns 1 and 3 and uses the CSI-RS pattern 2 for CSI-RStransmission in a specific subframe. In this case, referring to FIG. 6,the BS may transmit muting configuration information specifying that theCSI-RS pattern 1 is a starting CSI-RS pattern and the CSI-RS pattern 3is an ending CSI-RS pattern. In addition, the BS may transmit CSI-RSpattern information indicating that the CSI-RS pattern 2 is used forCSI-RS transmission of the BS to a UE within the corresponding coverage.The CSI-RS pattern 1 and the CSI-RS pattern 3 may be used for CST-RStransmission of another cell that is adjacent to a cell in which the UEto which the muting configuration information and the CSI-RS patterninformation are transmitted is located.

The UE, which has received the muting configuration information and theCSI-RS pattern information, can determine that a signal received throughthe CSI-RS patterns 1 and 3 is excluded from data in the rate matchingand RE mapping procedures. Based on the muting configuration informationand the CSI-RS pattern information, the UE assumes that no downlinksignal is transmitted through the CSI-RS pattern 1 and the CSI-RSpattern 3 and a CSI-RS of the BS is transmitted through the CSI-RSpattern 2. That is, the UE assumes that the BS performs transmissionthrough resources corresponding to the CSI-RS pattern 1 and the CSI-RSpattern 3 with zero transmission power and performs transmission throughresources corresponding to the CSI-RS pattern 2 with nonzerotransmission power for CSI-RS transmission.

According to the second embodiment of the present invention, when atotal of n CSI-RS patterns have been defined, the number of mutingpatterns that can be configured by the BS is (n(n+1)/2), including thecase in which no CSI-RS pattern is muted. The BS may signal a mutedCSI-RS to the UE by transmitting, to the UE, one of the (n(n+1)/2)muting patterns using ceiling {log₂(n(n+1)/2)} bits.

In the case where the BS signals the starting CSI-RS pattern index andthe ending CSI-RS pattern index as muting configuration information tothe UE as described above, overhead caused by signaling of the mutingconfiguration information may be reduced compared to that of signalingof the bitmap. However, according to the second embodiment, flexibilityof the CSI-RS configuration is limited since consecutive CSI-RS patternsshould always be configured for channel measurement and/or interferencemeasurement.

Third Embodiment: Number-Based Muting Configuration

In the third embodiment of the present invention, consecutive CSI-RSpatterns from among predefined CSI-RS patterns are selected as CSI-RSpatterns for channel measurement and/or interference measurement whileCSI-RS pattern 0 is always set as a starting CSI-RS pattern. The thirdembodiment of the present invention is a special case of the secondembodiment of the present invention. In this case, the BS may transmitinformation indicating an ending CSI-RS pattern or informationindicating the number of CSI-RS patterns that are muted as mutingconfiguration information to the UE.

FIG. 7 illustrates resource muting and muting configuration informationaccording to the third embodiment of the present invention.

The BS may configure resource muting so as to mute two CSI-RS patterns,starting from the CST-RS pattern 0. The BS may transmit informationindicating that the number of CSI-RS patterns to be muted is 2 as mutingconfiguration information to the corresponding coverage.

A UE located in the coverage may receive the muting configurationinformation and determine from the received muting configurationinformation that the BS does not transmit a downlink signal through thetwo CSI-RS patterns including the CSI-RS pattern 0, i.e., the CSI-RSpattern 0 and the CSI-RS pattern 1. The UE performs rate matching,assuming based on the muting configuration information that the BStransmits no signal through the REs belonging to the range of CSI-RSpatterns from the CSI-RS pattern 0 to the CSI-RS pattern 2. Accordingly,the UE excludes a signal received through the CSI-RS pattern 0 and theCSI-RS pattern 2 from a data demodulation procedure.

FIG. 8 illustrates another example of resource muting and mutingconfiguration information according to the third embodiment of thepresent invention.

A wireless communication system may be configured so as to allow cellsbelonging to a specific estimation set to use consecutive CSI-RSpatterns. In this case, BS(s) that participate in channel measurementand/or interference measurement may configure consecutive CSI-RSpatterns starting from the CSI-RS pattern 0 according to the number ofcells belonging to the estimation set. The BS may transmit informationindicating the number of the configured CSI-RS patterns or informationindicating the number of muted CSI-RS patterns as muting configurationinformation to the corresponding coverage. The BS also transmits CSI-RSpattern information indicating a CSI-RS pattern used for CSI-RStransmission from among the configured configuration CSI-RS patterns.

For example, let us assume that the BS configures consecutive CSI-RSpatterns 0, 1, and 2 for channel measurement and/or interferencemeasurement in a geographical region/space managed by the BS while theBS mutes the CSI-RS patterns 0 and 2 and uses the CSI-RS pattern 1 forCSI-RS transmission. In this case, referring to FIG. 8, the BS transmitsinformation indicating the number of CSI-RS patterns muted by the BS orthe number of CSI-RS patterns configured by the BS as mutingconfiguration information. In addition, the BS transmits CSI-RS patterninformation indicating that the BS performs CSI-RS transmission throughthe CSI-RS pattern 1 to a UE within the corresponding coverage.

The UE, which has received the muting configuration information and theCSI-RS pattern information, can determine that a signal received throughthe CSI-RS patterns 0 to 2 is excluded from data through rate matching.Based on the muting configuration information and the CSI-RS patterninformation, the UE assumes that no downlink signal is transmittedthrough the CSI-RS pattern 0 and the CSI-RS pattern 2 and a CSI-RS ofthe BS is transmitted through the CST-RS pattern 1. That is, the UEassumes that the BS performs transmission through resourcescorresponding to the CSI-RS pattern 0 and the CSI-RS pattern 2 with zerotransmission power and performs transmission through resourcescorresponding to the CSI-RS pattern 1 with CSI-RS transmission power.

According to the third embodiment of the present invention, when a totalof n CSI-RS patterns have been defined, the BS may transmit the mutingconfiguration information using ceiling {log₂(n)} bits. Accordingly,downlink overhead for muting configuration information may be reducedbeyond what was obtained in the second embodiment. However, according tothe third embodiment, flexibility of the CSI-RS configuration is morelimited than in the second embodiment since consecutive CSI-RS patterns,starting from the CSI-RS pattern 0, should always be configured forchannel measurement and/or interference measurement.

Table 1 shows comparison of the number of configurable muting patterns(=the number of RE mapping patterns) and the number of signaling bits ofmuting configuration information according to the first to thirdembodiments. From the viewpoint of rate matching, REs belonging to aCSI-RS pattern that the BS uses for CSI-RS transmission should behandled as non-data REs and therefore the number of patterns for ratematching (hereinafter referred to as rate matching patterns) may bedefined by the number of CSI-RS patterns. Accordingly, in Table 1, thenumber of rate matching patterns can be considered the number ofavailable CSI-RS patterns. In Table 1, it is assumed that the number ofavailable CSI-RS patterns for each number of CSI-RS ports is as shown inFIG. 3.

TABLE 1 Number of Number of Number of rate Number of RE CSI-RS Signalingsignaling matching mapping ports methods bits patterns patterns 2Bitmap-based 20 20 1048575 Tree-based 8 20 210 Number-based 5 20 30 4Bitmap-based 10 10 1023 Tree-based 6 10 55 Number-based 4 10 10 8Bitmap-based 5 5 31 Tree-based 4 5 15 Number-based 3 5 5

From Table 1, it can be seen that the signaling overhead for mutingconfiguration information is highest in the bitmap-based configurationof the first embodiment and is lowest in the number-based configurationof the third embodiment. However, the flexibility in the CSI-RS patternconfiguration for channel measurement and/or interference measurement ishighest in the first embodiment and is lowest in the third embodiment.

Fourth Embodiment: Group-Based CSI-RS Configuration

In the fourth embodiment of the present invention, CSI-RS patterns aregrouped and CSI-RS patterns for channel measurement and/or interferencemeasurement are configured from among CSI-RS patterns of one of thegroups.

For example, let us assume that the number of CSI-RS patterns availablefor CSI-RS transmission through 4 antenna ports is 10 and the number ofCSI-RS patterns available for CSI-RS transmission through 8 antennaports is 5. In this case, CSI-RS pattern indices {0, 1, 2, 3, 4, 5, 6,7, 8, 9} can be used for CSI-RS transmission through the 4 antenna portsand CSI-RS pattern indices {0, 1, 2, 3, 4} can be used for CSI-RStransmission through the 8 antenna ports in a subframe.

Table 2 illustrates CSI-RS pattern groups and muting configurationinformation according to the group-based muting configuration accordingto the fourth embodiment of the present invention. Specifically, Table 2shows the case in which the same size of CSI-RS pattern groups areconfigured regardless of the number of antenna ports. Table 2 is onlyillustrative and the size of each CSI-RS pattern group and CSI-RSpatterns belonging to each group may be defined differently from Table2.

TABLE 2 Number of CSI-RS Bitmap with ports CSI-RS pattern group(s)CSI-RS group 8 Group 1: {0, 1, 2, 3, 4} 4-bit {x, x, x, x}, x: 0 or 1 4Group 1: {0, 1, 2, 3, 4}Group 2: {5, 4-bit {x, x, x, x}, 6, 7, 8, 9} x:0 or 1 2 Group 1: {0, 1, 2, 3, 4}Group 2: {5, 4-bit {x, x, x, x}, 6, 7,8, 9}Group 3: {10, 11, 12, 13, x: 0 or 1 14}Group 4: {15, 16, 17, 18,19}

In the case where only one CSI-RS pattern group can be used for 8antenna ports and 2 CST-RS pattern groups can be used for 4 antennaports, a muted CST-RS pattern in a CSI-RS pattern group may be allocatedin a bitmap manner. In the case where a CSI-RS pattern group includes NCSI-RS patterns, N−1 bits are needed to indicate which CSI-RS pattern isused for resource muting from among the CSI-RS pattern groups since oneof the N CSI-RS patterns is used for CSI-RS transmission of the servingcell. For example, if N is 5, at least 4 bits are needed to indicate amuted CSI-RS pattern in the CSI-RS pattern group.

Referring to Table 2, 2 CSI-RS pattern groups (group 1: {0, 1, 2, 3, 4}and group 2: {5, 6, 7, 8, 9}) can be defined for 4 antenna ports. Inthis case, if the BS uses the CSI-RS pattern 5 for CSI-RS transmissionof the serving cell, the serving cell belongs to the CSI-RS patterngroup 2 and the 4-bit bitmap may indicate a CSI-RS pattern that is mutedamong the remaining CSI-RS patterns 6 to 9. For example, if the 4-bitbitmap indicates {0, 0, 1, 1}, the 4-bit bitmap may mean that the CSI-RSpattern 8 and the CSI-RS pattern 9 are used for resource muting.

Although Table 2 illustrates the case in which a bitmap-based mutingconfiguration is applied to the group-based muting configuration, thetree-based muting configuration and the number-based mutingconfiguration may also be applied to the group-based mutingconfiguration according to the fourth embodiment of the presentinvention.

Table 3 illustrates another example of muting configuration informationand CSI-RS pattern groups according to the group-based mutingconfiguration according to the fourth embodiment of the presentinvention. Specifically, in Table 3, different sizes of CSI-RS patterngroups are configured depending on the number of antenna ports. Table 3is only illustrative and the size of each CSI-RS pattern group andCSI-RS patterns belonging to each group may be defined differently fromTable 3.

TABLE 3 Number of Indication of CSI-RS CSI-RS pattern for RE mutingports CSI-RS pattern group(s) within CSI-RS pattern group 8 Group 1: {0,1, 2, 3, 4} Bitmap/tree/number-based 4 Group 1: {0, 1, 2, 3, 4, 5,Bitmap/tree/number-based 6, 7, 8, 9} 2 Group 1: {0, 1, 2, 3, 4, 5,Bitmap/tree/number-based 6, 7, 8, 9}Group 2: {10, 11, 12, 13, 14, 15,16, 17, 18, 19}

The size of each CSI-RS pattern group may be defined in various manners.For example, the size of each CSI-RS pattern group may be predefinedaccording to the number of antenna ports of the serving cell and may beconfigured in an upper layer signaling or a broadcast channel.

According to the fourth embodiment of the present invention, it ispossible to keep the number of CSI-RS patterns that can be used by aspecific cell equal to or less than a desired number since CSI-RSpatterns that can be used by the specific cell are limited within aspecific CSI-RS pattern group. Thus, according to the fourth embodimentof the present invention, it is possible to keep signaling overhead formuting configuration information transmission equal to or less than adesired level. However, if the size of the CSI-RS pattern group is toosmall, the flexibility of CSI-RS configuration is reduced since thenumber of CSI-RS patterns that can be selected by the BS is reduced. Onthe other hand, if the size of the CSI-RS pattern group is too large,the effect of a reduction in the overhead for muting configurationinformation signaling may not be very great although the number ofcombinations of CSI-RS patterns that can be selected by the BS isincreased.

Fifth Embodiment: Muting Configuration Based on a Specific Number ofAntenna Ports

In the fifth embodiment of the present invention, a CSI-RS pattern ismuted based on CSI-RS patterns defined for a specific number of CSI-RSports regardless of the actual number of antenna ports configured in theB S.

When the fifth embodiment of the present invention is applied, awireless communication system may be configured such that CSI-RSpatterns defined for a large number of CSI-RS ports are used forresource muting. This is because signaling overhead when CSI-RS patternsdefined for a large number of CSI-RS ports are used for resource mutingis reduced compared to when CSI-RS patterns defined for a small numberof CSI-RS ports are used for resource muting.

FIGS. 9 to 11 illustrate resource muting and muting configurationinformation according to the fifth embodiment of the present invention.

Referring to FIG. 9, let us assume that a muting pattern is definedbased on CST-RS patterns defined for 8 CSI-RS ports (hereinafterreferred to as 8Tx CSI-RS patterns). When the number of antenna ports ofcell A and the number of antenna ports of cell B are each 2, the cell Aand the cell B transmit a CSI-RS for each antenna port. That is, thecell A and the cell B each transmit two CSI-RSs. In the case whereCSI-RSs are configured such that a CSI-RS of the cell A is transmittedthrough a 2Tx CSI-RS pattern 1 which is a pattern for 2 CSI-RStransmission of FIG. 9(a) (hereinafter referred to as a 2Tx CST-RSpattern) and a CST-RS of the cell B is transmitted through a 2Tx CSI-RSpattern 12 of FIG. 9(a), a BS of the cell B (hereinafter referred to asa BS B) may configure, as a muting pattern, an 8Tx CSI-RS pattern 1including resources of the 2Tx CSI-RS pattern 1 of FIG. 9(a) configuredfor CSI-RS transmission of the cell A from among 5 8Tx CSI-RS patternsshown in FIG. 9(b).

The BS B may transmit information indicating that the 2Tx CSI-RS pattern12 is used for CSI-RS transmission and information indicating that the8Tx CSI-RS pattern 1 is muted from among the 5 8Tx CSI-RS patterns forthe 8 CSI-RS ports to a UE located in the cell B (hereinafter referredto as a UE B). By receiving the information, the UE B may determine thatthe BS does not transmit a signal through resources other than theresources corresponding to the 2Tx CSI-RS pattern 12 from amongresources corresponding to the 8Tx CSI-RS pattern 1.

If, for 2 CSI-RS ports and 4 CSI-RS ports, resource muting is configuredbased on CSI-RS patterns defined for 8 CSI-RS ports, i.e., based on 8TxCSI-RS patterns defined for 8 CSI-RS transmission in the above manner,signaling overhead is not substantial even when muting configurationinformation is transmitted according to the first embodiment which hasthe highest transmission overhead of muting configuration informationamong the first to third embodiments. Referring to FIG. 9(b), it ispossible to indicate a CSI-RS pattern(s) muted through a 5-bit bitmapsince the number of CSI-RS patterns available for resource muting is 5.

However, in the case in which the number of CSI-RS ports of each cell inthe estimation set is less than 8, muting overhead is increased sinceresources that are not actually used for CSI-RS transmission are alsomuted. Since the muted resources are not used for data transmission,this leads to a loss in the system throughput. However, in the presentinvention, a CSI-RS is not transmitted in every subframe but instead aCSI-RS is transmitted at intervals of a predetermined duty cyclecorresponding to a plurality of subframes. That is, overhead for CSI-RStransmission is small since a CSI-RS is transmitted only in subframes,which are at intervals of the predetermined transmission period, ratherthan be transmitted in every subframe. Generally, the wirelesscommunication system handles a control signal as being more importantthan a data signal. If the UE has failed to correctly receive a controlsignal, the UE cannot properly perform rate matching until the BSretransmits the control signal to the UE. This leads to delay or failureof data demodulation. Accordingly, a control signal is generallytransmitted at a coding rate lower than that of a data signal.Therefore, transmission of an amount of control signal requires agreater amount of radio resources than transmission of the same amountof data signal. On the other hand, even when the UE has failed tocorrectly receive a data signal, the UE can again receive the datasignal. In addition, even when part of a data signal is lost ordefective, the data signal is more likely to be properly demodulatedusing the remaining part than is the control signal. Taking intoconsideration this fact, it is possible to ignore loss due to resourcemuting for correct transmission of CSI-RSs of cells belonging to theestimation set.

However, taking into consideration that, currently, there are not manyBSs that implement up to 8 transmit antennas, it is possible toconfigure resource muting based on CSI-RS patterns defined for 4 CSI-RSports (hereinafter referred to as 4Tx CSI-RS patterns) rather than basedon 8Tx CSI-RS patterns which are CSI-RS patterns defined for 8 CSI-RSports. Referring to FIG. 10, let us assume that a muting pattern isdefined based on the 4Tx CSI-RS patterns defined for 4 CSI-RS ports. Inaddition, similar to FIG. 9, let us assume that the number of antennaports of each of the cell A and the cell B is 2 and CSI-RS transmissionis configured such that a CSI-RS of the cell A is transmitted through a2Tx CSI-RS pattern 1 of FIG. 10(a) (=the 2Tx CSI-RS pattern 1 of FIG.9(a)) and a CSI-RS of the cell B is transmitted through a 2Tx CSI-RSpattern 12 of FIG. 10(a) (=the 2Tx CSI-RS pattern 12 of FIG. 9(a)). Inthis case, the BS B can configure, as a muting pattern, a 4Tx CSI-RSpattern 1 including resources of the 2Tx CSI-RS pattern 1 configured forCSI-RS transmission of the cell A from among the 10 4Tx CSI-RS patternsof FIG. 10(b). In the case of FIG. 10, the BS B may mute only 2 REs foreach predetermined resource region for CSI-RS transmission of the cellA. Muting overhead of the embodiment of FIG. 10 is less than that of theembodiment of FIG. 9 since the BS B mutes 6 REs for each predeterminedresource region for CSI-RS transmission of the cell A. That is, in thecase where resources are muted based on the 4Tx CSI-RS patterns definedfor the 4 CSI-RS ports, the muting overhead is reduced compared to whenresources are muted based on the 8Tx CSI-RS patterns defined for the 8CSI-RS ports although the number of bits required for signaling ofmuting configuration information is increased.

In another example, referring to FIG. 11, a muting pattern is definedbased on 4Tx CSI-RS patterns defined for 4 CSI-RS ports, similar to FIG.10. However, in FIG. 11, it is assumed that the number of CSI-RS portsof the cell A is 2 and the number of CSI-RS ports of the cell B is 8 andCSI-RSs of the cell A is transmitted through a 2Tx CSI-RS pattern 1 ofFIG. 11(a) (=the 2Tx CSI-RS pattern 1 of FIG. 10(a) and FIG. 9(a)) andCSI-RSs of the cell B is transmitted through an 8Tx CST-RS pattern 3 ofFIG. 11(c). In this case, through the 2Tx CSI-RS pattern 1 of FIG.11(a), the BS A transmits CSI-RSs for channel measurement of the cell A.The BS A sets, to zero, transmission power of resources belonging to the4Tx CSI-RS patterns 3 and 8 of FIG. 11(b) corresponding to the 8TxCSI-RS pattern 3 of FIG. 11(c) that the BS B uses for CSI-RStransmission. That is, the BS A mutes the 4Tx CSI-RS patterns 3 and 8 ofFIG. 11(b). The BS B transmits 8 CSI-RSs for channel measurement of thecell B through the 8Tx CST-RS pattern 3 of FIG. 11(c). Since the 2TxCSI-RS pattern 1 of FIG. 11(a) that the BS A uses for CSI-RStransmission is in an inclusion relationship with the 4Tx CSI-RS pattern1 of FIG. 11(b), the BS B sets transmission power of resources belongingto the 4Tx CSI-RS pattern 1 of FIG. 11(b) to zero. That is, the BS Bmutes not only resources of subcarrier index 11 and OFDM symbol indices9 and 10 but also resources of subcarrier index 5 and OFDM symbolindices 9 and 10 even when only resources of subcarrier index 11 andOFDM symbol indices 9 and 10 among the resources of a resource regionincluding 12 subcarriers and 14 OFDM symbols are used for CSI-RStransmission by the BS A.

Taking into consideration that CSI-RS patterns are defined for eachnumber of CSI-RS ports, information indicating the number of CSI-RSports for which CSI-RS patterns used for a muting pattern have beendefined needs to be also transmitted to the UE in order to specify themuting pattern in the first to fourth embodiments. On the other hand, inthe fifth embodiment, the number of antenna ports used as a referencefor resource muting does not need to be separately signaled since CSI-RSpatterns defined for a specific number of antenna ports are used forresource muting. Accordingly, according to the fifth embodiment,transmission overhead of muting configuration information may be reducedcompared to the first to third embodiments. In addition, according tothe fifth embodiment, the BS can select a CSI-RS pattern required forCSI-RS transmission of a specific cell from among all CSI-RS patternsdefined for a number of antenna ports corresponding to the specific cellunless the CSI-RS pattern does not overlap with CSI-RS patterns ofanother cell. Thus, according to the fifth embodiment, the BS canconfigure resource muting and CSI-RS transmission with high flexibilityand considerable freedom.

The fifth embodiment may be used in combination with one of the first tothird embodiments. For example, referring to FIG. 10, the BS A maysignal the fact that the 4Tx CSI-RS pattern 1 is muted to a UE locatedin the cell A by setting, to “1”, a bit corresponding to the CSI-RSpattern 1 in the bitmap of 10 bits which are in one-to-onecorrespondence with 10 4Tx CSI-RS patterns defined for 4 CSI-RS ports.

In another example, referring to FIG. 11, the BS A may transmit, to theUE A, a bitmap of “00100000100” configured by setting, to “1”, bitscorresponding to the CSI-RS patterns 3 and 8 among 10 bits which are inone-to-one correspondence with 10 4Tx CSI-RS patterns defined for 4CSI-RS ports. The BS B may transmit, to the UE B, a bitmap of“00100000000” configured by setting, to “1”, a bit corresponding to theCSI-RS pattern 1. In the case where the UE has received a bitmap set to“0010000100”, the UE may receive a downlink transmission signal,assuming that transmission power for resources corresponding to theCSI-RS patterns 3 and 8 among 10 4Tx CSI-RS patterns of FIG. 11(b) iszero. In the case where the UE has been set to “0100000000”, the UEassumes that transmission power for resources corresponding to the 104Tx CSI-RS patterns 1 of FIG. 11(b) is zero.

<CSI-RS Configuration Signaling and Muting Pattern Signaling>

CSI-RS patterns of a cell are cell-specific parameters and are used in astatic manner without change once the CSI-RS patterns are allocated tothe cell. On the other hand, resource muting is used only when the UE isa specific situation such as a multi-cell transmission mode (forexample, a Coordinate Multi-Point (CoMP)). Accordingly, resource mutingneeds to be able to be turned on/off according to the situation. Takinginto consideration this situation, to reduce the complexity of UEimplementation, a CSI-RS configuration may be transmitted through abroadcast channel (for example, a Maser Information Block (MIB), SystemInformation Block 1 (SIB-1), or System Information Block 2 (SIB-2)) suchthat the UE does not need to continue monitoring the CSI-RS patternindex of the serving cell once the UE acquires the CSI-RS pattern indexof the serving cell. However, CSI-RS patterns that are muted in theserving cell may be turned on/off and may also be changed in the timedomain. Accordingly, it may be more desirable that informationindicating CSI-RS patterns that are muted be transmitted to the UEthrough higher layer signaling or RRC signaling so as to allow the BS toconfigure the CSI-RS patterns that are muted.

FIG. 12 is a block diagram of a UE and a BS for implementing the presentinvention.

The UE operates as a transmitting device in uplink and operates as areceiving device in downlink. On the other hand, the BS may operate as areceiving device in uplink and may operate as a transmitting device indownlink.

The UE and the BS include antennas 500 a and 500 b for receivinginformation, data, signals, and/or messages, transmitters 100 a and 100b for transmitting messages by controlling the antennas 500 a and 500 b,receivers 300 a and 300 b for receiving messages by controlling theantennas 500 a and 500 b, and memories 200 a and 200 b for storingvarious information associated with communication in the wirelesscommunication system, respectively. The UE and the BS further includeprocessors 400 a and 400 b, respectively, which are configured toperform the present invention by controlling the components of the UEand the BS such as the transmitters 100 a and 100 b, the receivers 300 aand 300 b, and the memories 200 a and 200 b. The transmitter 100 a, thememory 200 a, the receiver 300 a, and the processor 400 a in the UE maybe configured as independent components on separate chips or two or morecomponents in the UE may be implemented through a single chip.Similarly, the transmitter 100 b, the memory 200 b, the receiver 300 b,and the processor 400 b in the BS may be configured as independentcomponents on separate chips or two or more components in the BS may beimplemented through a single chip. The transmitter and the receiver mayalso be configured as a single transceiver in the UE or the BS.

The antennas 500 a and 500 b transmit signals generated by thetransmitters 100 a and 100 b to the outside, or transfer radio signalsreceived from the outside to the receivers 300 a and 300 b. The antennas500 a and 500 b may also be referred as antenna ports. Each antenna portmay correspond to one physical antenna or may be configured as acombination of two or more physical antenna elements. A signaltransmitted from each antenna port cannot be further deconstructed bythe receiver 300 a of the UE. A reference signal transmitted inassociation with a corresponding antenna port defines the correspondingantenna port from the viewpoint of the UE and enables the UE to performchannel estimation for the antenna port, regardless of whether or notthe channel is a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna port. That is, in the present invention, theantenna port is defined such that a channel for transmitting a symbol onthe antenna port can be derived from the channel through which adifferent symbol on the same antenna port is transmitted. In the casewhere the transmitters 100 a and 100 b and/or the receivers 300 a and300 b support a Multiple Input Multiple Output (MIMO) function whichtransmits and receives data using a plurality of antennas, each of thetransmitters 100 a and 100 b and/or the receivers 300 a and 300 b may beconnected to two or more antennas.

The processors 400 a and 400 b generally control overall operations ofthe modules of the UE and the BS. Especially, the processors 400 a and400 b may carry out various control functions for performing the presentinvention, a Medium Access Control (MAC) frame variable control functionaccording to service characteristics and radio environments, a powersaving mode function for controlling idle-mode operations, a handoverfunction, and an authentication and encryption function. The processors400 a and 400 b may also be referred to as controllers,microcontrollers, microprocessors, microcomputers, etc. The processors400 a and 400 b may be configured by hardware, firmware, software, or acombination thereof. In the case where the present invention isimplemented by hardware, the processors 400 a and 400 b may includeApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), and/or Field Programmable Gate Arrays(FPGAs) configured to implement the present invention. In the case wherethe present invention is implemented by firmware or software, firmwareor software may be configured so as to include a module, a procedure, afunction, etc., for performing functions or operations of the presentinvention. This firmware or software configured to perform the presentinvention may be provided in the processors 400 a and 400 b, or may bestored in the memories 200 a and 200 b and driven by the processors 400a and 400 b.

The transmitters 100 a and 100 b perform predetermined coding andmodulation for signals and/or data, which are scheduled by schedulersconnected to the processors 400 a and 400 b and transmitted to theoutside, and then transfer the resulting signals and/or data to theantennas 500 a and 500 b. For example, the transmitters 100 a and 100 bconvert a data stream, which is to be transmitted, into K layers throughdemultiplexing, channel coding, modulation, etc. The K layers aretransmitted through the antennas 500 a and 500 b via transmissionprocessors in the transmitters 100 a and 100 b. The transmitters 100 aand 100 b and the receivers 300 a and 300 b of the UE and the BS may beconfigured in different manners depending on the procedures ofprocessing transmitted and received signals.

The memories 200 a and 200 b may store programs required for processingand control of the processors 400 a and 400 b and may temporarily storeinput and output information. Each of the memories 200 a and 200 b maybe implemented using a flash memory-type storage medium, a harddisk-type storage medium, a multimedia card micro-type storage medium, acard-type memory (e.g. a Secure Digital (SD) or eXtreme Digital (XS)memory), a Random Access Memory (RAM), a Static Random Access Memory(SRAM), a Read-Only Memory (ROM), an Electrically Erasable ProgrammableRead-Only Memory (EEPROM), a Programmable Read-Only Memory (PROM), amagnetic memory, a magnetic disc, an optical disc, or the like.

The BS processor 400 b according to the embodiments of the presentinvention may configure CSI-RS subframes and CSI-RS patterns. The BSprocessor 400 b may generate information indicating the configuredCSI-RS subframes, i.e., CSI-RS subframe configuration information. TheBS processor 400 b may generate information indicating a CSI-RS subframein a radio frame and a CSI-RS transmission period as the CSI-RS subframeconfiguration information. The BS processor 400 b may control the BStransmitter 100 b so as to transmit the CSI-RS subframe configurationinformation. The BS processor 400 b may generate information indicatingthe configured CSI-RS pattern, i.e., CSI-RS pattern information. The BSprocessor 400 b may generate a CSI-RS pattern index corresponding to theconfigured CSI-RS pattern as the CSI-RS pattern information. The BSprocessor 400 b may control the BS transmitter 100 b so as to transmitthe CSI-RS pattern information. The BS processor 400 b may generateinformation indicating the number of antenna ports for CSI-RStransmission, i.e., information indicating the number of CSI-RS ports,as the CSI-RS pattern information and control the BS transmitter 100 bto transmit the number-of-CSI-RS-ports information to the UE. The BSprocessor 400 b controls the BS transmitter 100 b so as to transmit aCSI-RS(s) according to the CSI-RS pattern in the CSI-RS subframe. Inthis case, each CSI-RS port of the BS transmits a corresponding CSI-RSthrough a CSI-RS RE for the CSI-RS port in the CSI-RS pattern.

One or more CST-RS ports may be configured for a given cell. A BS of theserving cell (hereinafter referred to as a serving BS) may configure oneor more CSI-RS ports for channel measurement of the serving cell and maytransmit one or more CSI-RSs through the one or more CSI-RS portsaccording to a CSI-RS pattern. For example, referring to FIG. 10(c), aBS (hereinafter referred to as a BS A) to which a cell A belongs mayconfigure 2 CSI-RS ports and may transmit, to a UE located in the cellA, 2 CSI-RSs on the 2Tx CSI-RS pattern 1 through the 2 CSI-RS ports.

In the case where an adjacent cell upon which the serving cell has agreat influence or which has a great influence upon the serving cell ispresent, the serving BS may mute a downlink signal on REs belonging to aCSI-RS pattern that the adjacent cell uses for CSI-RS transmission. Forexample, referring to FIGS. 10(c) and 10(d), in the case where a cell Bwhich uses a 2Tx CSI-RS pattern 12 for CSI-RS transmission is presentadjacent to the cell A, CSI-RS ports of the BS A may transmit CSI-RSs onREs belonging to the 2Tx CSI-RS pattern 1 and transmit no signal on REsbelonging to the 2Tx CSI-RS pattern 12.

The serving BS may transmit information indicating a CSI-RS pattern inwhich signals of the serving cell are muted to the UE according to oneof the above embodiments of the present invention. However, resourcemuting may not be configured in the case where only an adjacent cellupon which the serving cell has little influence or which has littleinfluence upon the serving cell is present.

Resource muting may be configured according to a specific period,similar to CSI-RS transmission. That is, resources corresponding to aCSI-RS pattern configured for muting may be muted only in a subframecorresponding to the specific period rather than be muted in everysubframe. Resource muting is generally configured to increase CSI-RStransmission efficiency and, taking into consideration the fact thatresource muting is accompanied by loss of data throughput, it isdesirable that a CSI-RS pattern be muted only in a specific subframerather than being muted in every subframe.

The muting subframe including the muted CSI-RS pattern and the resourcemuting period may be configured equal to or different from the CSI-RSsubframe. When the muting subframe is identical to the CSI-RS subframe,the BS may not separately transmit information specifying the mutingsubframe to the UE. When the CSI-RS subframe and the muting subframe areconfigured independent of each other, the BS may separately configureinformation specifying the CSI-RS subframe configured for CSI-RStransmission of the serving cell and information specifying the subframein which muting is configured and transmit the configured information tothe UE.

The BS processor 400 b according to the embodiments of the presentinvention may configure a subframe for resource muting. The BS processor400 b may generate information indicating the configured mutingsubframe, i.e., muting subframe configuration information. The BSprocessor 400 b may control the BS transmitter 100 b to transmit themuting subframe configuration information.

The BS processor 400 b may configure a CSI-RS pattern for resourcemuting according to an embodiment of the present invention.

For example, the BS processor 400 b configured according to the fifthembodiment may configure resource muting based on CSI-RS patternsconfigured for a specific number of antenna ports regardless of thenumber of antenna ports provided to the BS. Referring to FIG. 10, the BSprocessor 400 b of the fifth embodiment may configure resource mutingusing 4Tx CSI-RS patterns defined for 4 CSI-RS ports regardless ofCSI-RS ports of the corresponding cell. That is, the BS processor 400 bconfigured according to the embodiment of FIG. 10 always configuresresource muting in units of 4Tx CSI-RS patterns even when the number ofCSI-RS ports of the corresponding cell is 2 or 8. In another example,the BS processor 400 b configured according to the second embodiment mayconfigure one or more consecutive CSI-RS patterns among n availableCSI-RS patterns as CSI-RS patterns for resource muting.

The BS processor 400 b may generate information indicating CSI-RSpatterns configured for muting, i.e., muting configuration information,according to an embodiment of the present invention. For example,referring to FIG. 10, the processor of the BS A may generate a bitmap of10 bits set to “0100000000” according to the first and fifthembodiments. Here, it is assumed that the Most Significant Bit (MSB)corresponds to the minimum CSI-RS pattern index among the 10 CSI-RSpattern indices and subsequent bits in the bitmap correspondrespectively to CSI-RS patterns in increasing order. In another example,referring to FIG. 6, the BS processor 400 b configured according to thesecond embodiment may generate muting pattern indices corresponding tothe starting CSI-RS pattern 1 and the ending CSI-RS pattern 3 as mutingconfiguration information.

The BS processor 400 b may control the BS transmitter 100 b so as totransmit the muting configuration information. The BS processor 400 bmay control the BS transmitter 100 b so as to mute REs belonging to themuted CSI-RS pattern in the muting subframe. That is, the BS processor400 b may control the BS transmitter 100 b such that transmission powerof REs belonging to the muted CSI-RS pattern in the muting subframe is0. In this case, each transmit antenna 500 b of the BS transmits asignal with zero transmission power through REs belonging to the mutedCSI-RS pattern in the muting subframe. However, when a CSI-RS resourceused for CSI-RS transmission of the corresponding cell is present amongresources belonging to the muted CSI-RS pattern, the BS processor 400 bdoes not mute the CSI-RS resource.

The UE receiver 300 a receives the muting configuration information fromthe BS and transfers the muting configuration information to the UEprocessor 400 a. The UE processor 400 a may identify a correspondingresource in a specific resource region based on the muting configurationinformation. For example, in the case in which a CSI-RS pattern isdefined in a resource region including 12 subcarriers and 14 OFDMsymbols, the UE processor 400 a may determine a resource in which the BSdoes not perform downlink transmission in the resource region based onthe muting configuration information. For example, let us assume that amuted CSI-RS pattern is configured according to the fifth embodiment ofthe present invention and the muted CSI-RS pattern is indicatedaccording to the second embodiment. Referring to FIG. 10, in the casewhere a UE belonging to the cell A (hereinafter referred to a UE A)receives a bitmap of 10 bits set to “0100000000” from the BS A, theprocessor 400 a of the UE A may determine that signals transmitted bythe BS are not present in resources corresponding to the 4Tx CSI-RSpattern 1 among the 4Tx CSI-RS patterns of FIG. 10(b). However, sincethe resources corresponding to the 2Tx CSI-RS pattern 1 among resourcescorresponding to the 4Tx CSI-RS pattern 1 are used for CSI-RStransmission of the cell A, the processor 400 a of the UE A does notdetermine that such transmitted signals are absent in resourcescorresponding to the 2Tx CSI-RS pattern 1 of FIG. 10(a). Rather, theprocessor 400 a of the UE A may perform channel measurement using atransmitted signal in resources corresponding to the 2Tx CSI-RS pattern1 of FIG. 10(a). The processor of the UE A may determine that REscorresponding to CSI-RS patterns corresponding to the bits set to “0”are data REs if there is no other specific reason (for example, unlessthe resources are resources used for transmission of a reference signalsuch as transmission of a synchronous signal of the BS A and/or aCSI-RS/CRS/DRS by the BS A)

The UE processor 400 a may calculate channel state information from achannel measurement result and/or an interference measurement result andcontrol the UE transmitter 100 a to feed the channel state informationback to the BS.

Although the embodiments of the present invention have been describedwith reference to downlink transmission as an example, the embodimentsmay be applied to uplink transmission in the same manner. In the casewhere the embodiments of the present invention are applied to uplinktransmission, the operations performed by the BS in the aboveembodiments may be performed by the UE and the operations performed bythe UE in the above embodiments may be performed by the BS.

The detailed description of the preferred embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. Accordingly, the inventionshould not be limited to the specific embodiments described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention may be used for a BS, a UE, andvarious other equipment in a wireless communication system.

The invention claimed is:
 1. A method for transmitting, by a userequipment, channel state information, the method comprising: receiving,by the user equipment, zero power CSI-RS information indicating one ormore zero power CSI-RS resources for a serving cell; and transmitting,by the user equipment, the channel state information based on the zeropower CSI-RS information, wherein the user equipment presumes that nodownlink data is mapped to the one or more zero power CSI-RS resources,wherein the zero power CSI-RS information includes a bitmap having bitscorresponding respectively to CSI-RS resources defined for a fixednumber of antenna ports, regardless of a number of antenna ports used inthe serving cell, among a plurality of CSI-RS resources definedaccording to numbers of antenna ports, wherein the fixed number isgreater than two, wherein each of the plurality of CSI-RS resources isconfigured with one or more subcarriers by two consecutive OFDM symbolsin a resource block according to the numbers of antenna ports, andwherein the two consecutive OFDM symbols are OFDM symbols 5 and 6, OFDMsymbols 9 and 10, or OFDM symbols 12 and 13, among OFDM symbols 0 to 13included in the resource block.
 2. The method of claim 1, wherein theplurality of CSI-RS resources comprise: CSI-RS resources for two antennaports, each of which being configured with one subcarrier by the twoconsecutive OFDM symbols; CSI-RS resources for four antenna ports, eachof which being configured with two subcarriers by the two consecutiveOFDM symbols; and CSI-RS resources for eight antenna ports, each ofwhich being configured with four subcarriers by the two consecutive OFDMsymbols.
 3. The method of claim 1, wherein the zero power CSI-RSinformation includes a duty cycle at which the one or more zero powerCSI-RS resources occur.
 4. The method of claim 1, wherein the zero powerCSI-RS information includes start subframe information at whichoccurrence of the one or more zero power CSI-RS resources start.
 5. Themethod of claim 1, where the one or more zero power CSI-RS resourcesinclude a CSI-RS resource used for a CSI-RS of a neighboring cell. 6.The method of claim 5, further comprising performing, by the userequipment, channel measurement for the neighboring cell based on theCSI-RS of the neighboring cell and based on the one or more zero powerCSI-RS resources.
 7. A user equipment for transmitting channel stateinformation, the user equipment comprising: a transmitter; a receiver;and a processor configured to: control the transmitter and the receiver;control the receiver to receive zero power CSI-RS information indicatingone or more zero power CSI-RS resources for a serving cell; calculatethe channel state information based on the zero power CSI-RSinformation; control the transmitter to transmit the channel stateinformation; and presume that no downlink data is mapped to the one ormore zero power CSI-RS resources, wherein the zero power CSI-RSinformation includes a bitmap having bits corresponding respectively toCSI-RS resources defined for a fixed number of antenna ports, regardlessof a number of antenna ports used in the serving cell, among a pluralityof CSI-RS resources defined according to numbers of antenna ports,wherein the fixed number is greater than two, wherein each of theplurality of CSI-RS resources is configured with one or more subcarriersby two consecutive OFDM symbols in a resource block according to thenumbers of antenna ports, and wherein the two consecutive OFDM symbolsare OFDM symbols 5 and 6, OFDM symbols 9 and 10, or OFDM symbols 12 and13, among OFDM symbols 0 to 13 included in the resource block.
 8. Theuser equipment of claim 7, wherein the plurality of CSI-RS resourcescomprise: CSI-RS resources for two antenna ports, each of which beingconfigured with one subcarrier by the two consecutive OFDM symbols;CSI-RS resources for four antenna ports, each of which being configuredwith two subcarriers by the two consecutive OFDM symbols; and CSI-RSresources for eight antenna ports, each of which being configured withfour subcarriers by the two consecutive OFDM symbols.
 9. The userequipment of claim 7, wherein the zero power CSI-RS information includesa duty cycle at which the one or more zero power CSI-RS resources occur.10. The user equipment of claim 7, wherein the zero power CSI-RSinformation includes start subframe information at which occurrence ofthe one or more zero power CSI-RS resources start.
 11. The userequipment of claim 7, where the one or more zero power CSI-RS resourcesinclude a CSI-RS resource used for a CSI-RS of a neighboring cell. 12.The user equipment of claim 11, wherein the processor is furtherconfigured to perform channel measurement for the neighboring cell basedon the CSI-RS of the neighboring cell and based on the one or more zeropower CSI-RS resources.
 13. A method for receiving, by a base station,channel state information, the method comprising: transmitting, by thebase station, zero power CSI-RS information indicating one or more zeropower CSI-RS resources for a serving cell; and receiving, by the basestation, the channel state information measured based on the zero powerCSI-RS information, wherein the one or more zero power CSI-RS resourceshave no downlink data mapped to the one or more zero power CSI-RSresources, wherein the zero power CSI-RS information includes a bitmaphaving bits corresponding respectively to CSI-RS resources defined for afixed number of antenna ports, regardless of a number of antenna portsused in the serving cell, among a plurality of CSI-RS resources definedaccording to numbers of antenna ports, wherein the fixed number isgreater than two, wherein each of the plurality of CSI-RS resources isconfigured with one or more subcarriers by two consecutive OFDM symbolsin a resource block according to the numbers of antenna ports, andwherein the two consecutive OFDM symbols are OFDM symbols 5 and 6, OFDMsymbols 9 and 10, or OFDM symbols 12 and 13, among OFDM symbols 0 to 13included in the resource block.
 14. The method of claim 13, wherein theplurality of CSI-RS resources comprise: CSI-RS resources for two antennaports, each of which being configured with one subcarrier by the twoconsecutive OFDM symbols; CSI-RS resources for four antenna ports, eachof which being configured with two subcarriers by the two consecutiveOFDM symbols; and CSI-RS resources for eight antenna ports, each ofwhich being configured with four subcarriers by the two consecutive OFDMsymbols.
 15. The method of claim 13, wherein the zero power CSI-RSinformation includes a duty cycle at which the one or more zero powerCSI-RS resources occur.
 16. The method of claim 13, wherein the zeropower CSI-RS information includes start subframe information at whichoccurrence of the one or more zero power CSI-RS resources start.
 17. Abase station for receiving channel state information, the base stationcomprising: a transmitter, a receiver, and a processor configured to:control the transmitter and the receiver; control the transmitter totransmit zero power CSI-RS information indicating one or more zero powerCSI-RS resources for a serving cell; and control the receiver to receivethe channel state information measured based on the zero power CSI-RSinformation, wherein the one or more zero power CSI-RS resources have nodownlink data mapped to the one or more zero power CSI-RS resources,wherein the zero power CSI-RS information includes a bitmap having bitscorresponding respectively to CSI-RS resources defined for a fixednumber of antenna ports, regardless of a number of antenna ports used inthe serving cell, among a plurality of CSI-RS resources definedaccording to numbers of antenna ports, wherein the fixed number isgreater than two, wherein each of the plurality of CSI-RS resources isconfigured with one or more subcarriers by two consecutive OFDM symbolsin a resource block according to the numbers of antenna ports, andwherein the two consecutive OFDM symbols are OFDM symbols 5 and 6, OFDMsymbols 9 and 10, or OFDM symbols 12 and 13, among OFDM symbols 0 to 13included in the resource block.
 18. The base station of claim 17,wherein the plurality of CSI-RS resources comprise: CSI-RS resources fortwo antenna ports, each of which being configured with one subcarrier bythe two consecutive OFDM symbols; CSI-RS resources for four antennaports, each of which being configured with two subcarriers by the twoconsecutive OFDM symbols; and CSI-RS resources for eight antenna ports,each of which being configured with four subcarriers by the twoconsecutive OFDM symbols.
 19. The base station of claim 17, wherein thezero power CSI-RS information includes a duty cycle at which the one ormore zero power CSI-RS resources occur.
 20. The base station of claim17, wherein the zero power CSI-RS information includes start subframeinformation at which occurrence of the one or more zero power CSI-RSresources start.